Induced resistance in plants and the role of pathogenesis-related proteins

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Induced resistance in plants and the role of pathogenesis-related proteins

Loon, L.C. van

(1997) European Journal of Plant Pathology, volume 103, pp. 753 - 765

(Article)

Abstract

The nature of induced resistance
Resistance, according to Agrios (1988) is the ability
of an organism to exclude or overcome, completely
or in some degree, the effect of a pathogen or other
damaging factor. Disease resistance in plants is manifested
by limited symptoms, reflecting the inability
of the pathogen to grow or multiply and spread, and
often ... read more takes the form of a hypersensitive reaction (HR),
in which the pathogen remains confined to necrotic
lesions near the site of infection. Induced resistance is
the phenomenonthat a plant, once appropriately stimulated,
exhibits an enhanced resistance upon 'challenge'
inoculation with a pathogen. Although induced resistance
has been attracting attention recently (Ryals et
al., 1994; Hammerschmidt and Kuc, 1995), the first
systematic enquiry into induced resistance was made
by Ross (1961a,b). He observed that the inducible
resistance response to tobacco mosaic virus (TMV)
in N gene-containing, hypersensitively reacting tobacco
was not confined to the immediate vicinity of the
resulting local necrotic lesions, but extended to other
plant parts. A ring of tissue around the developing
lesions became fully refractory to subsequent infection
(localized acquired resistance; Ross, 1961a), whereas
challenge inoculation of distant tissues resulted in
much smaller, and occasionally fewer, lesions (systemic
acquired resistance (SAR); Ross, 1961b) than in
non-induced plants. Even leaves thatweremere initials
at the time of the primary inoculation became induced,
suggesting that as a result of the initial infection, a
signal was generated, transported and propagated, that
primed the plant to respond more effectively to subsequent
infection (Bozarth and Ross, 1964). Treatments that influenced lesion size after primary infection had
similar effects on lesions developing upon challenge
inoculation (Ross, 1966), leading to the conclusion
that the mechanisms responsible for resistance expression
were the same under both conditions. Only upon
challenge inoculation, defense mechanisms appeared
to be expressed earlier and to a greater extent (De Laat
and Van Loon, 1983; Dean and Kuc, 1987). show less